CBANIAL NEEVES. 273 



small ' pre-spiracular ' branches, one or more 

 of which pass to the anterior wall of the 

 spiracle and to the pseudobranch. 



8. The eighth or auditory nerve, immediately after its 



origin, enters the auditory capsule through a hole in 

 the anterior end of its inner wall, and divides into 

 branches supplying the several parts of the internal 

 ear. 



Slice aivay the auditory capsule down to the level of the 

 root of the aioditory nerve, and trace the nerve into it. 



9. The ninth or glosso-pharyngeal nerve arises from the side 



of the meduUa, about an eighth of an inch behind the 

 auditory nerve and nearer the ventral surface. It at 

 once enters a foramen on the inner side of the auditory 

 capsule and about the middle of its length, and, passing 

 horizontally outwards and backwards along a canal 

 in the floor of the capsule, emerges at its posterior 

 and outer angle, opposite the upper end of the first 

 branchial cleft, where it divides into two branches. 



i. The anterior or pre-branchial branch is the 

 smaller of the two, and runs down the pos- 

 terior border of the hyoid arch. 



ii. The posterior or post-branchial branch is larger, 

 and runs down the anterior border of the first 

 branchial arch. 



Press away the medulla from the skull-wall to see the root 

 of the nerve, about an eighth of an inch behind the auditory 

 nerve : slice away the auditory capsule horizontally to expose 

 the nerve in the canal, and then follow the branches along the 

 branchial arches. 



10. The pneumogastric nerve or vagus is a large nerve, 



which arises by a number of roots from the side of the 

 hinder part of the medulla. The root of the lateral- 

 line nerve is dorsal to that of the glosso-pharyngeal. 

 The vagus, accompanied for some distance by the 

 lateral-line nerve, runs outwards and backwards 



